Plant pathogens are similar to other living organisms in that they contain a degree
of genetic variability within their genes that govern physical structure and internal
biochemical activities. Any selection pressure imposed on a population of an organism
can result in visible and invisible changes within that population. Selective breeding
is a tool used to express the genetic diversity within a population of an organism,
as demonstrated by the proliferation of dog breeds or varieties of agricultural
crops when compared to their original ancestral forms. Other selection pressures
can result in unwanted changes within a population, such as the development of resistance
to antibiotics used to treat human and animal diseases and to plant protection chemistries
used to manage plant diseases. In our area, plant protection products are used primarily
against diseases caused by fungi. Specific recommendations have been established
by an organization called the Fungicide Resistance Action Committee to manage the
development of fungicide resistance within a target plant pathogen population. The
major resistance management strategies are as follows. 1.) Do not use a single mode
of action in isolation.
Instead, apply the material as a mixture or in alternation
with one or more fungicides with different modes of action within a treatment program.
2.) Restrict the number of applications of a particular mode-of-action
a season and only make applications when necessary. 3.) Do not apply less than the
manufacture’s recommended dose. 4.) Target fungicide applications for disease prevention
and not eradication. 5.) Use an integrated approach to disease management.
By employing these resistance management strategies as well as using disease-resistant
cultivars, biological control agents, crop rotation, and other beneficial cultural
practices, the end result can be a high level of disease control, lower amounts
of total fungicides needed, and decreased selection of fungicide-resistant components
within the pathogen population.
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